The present invention relates to devices utilizing the propagation of magnetostatic waves along a ferrimagnetic layer deposited on a substrate. Amongst these devices, there are some which operate by means of transducers in the form of microtapes to transmit or receive magnetostatic surface or volume waves. In particular, the invention relates to filter devices which, within a wide frequency range permit selective transmission of magnetostatic waves having a predetermined wavelength. As a matter of fact, magnetostatic wave devices are tunable by means of a magnetic field and may operate at a given wavelength while retaining the option of changing the frequency. The problem which arises is that of attenuating the transmission of the magnetostatic waves at wavelengths differing from a preselected value, this problem being encountered in particular applications in which a reflector network or a cavity resonator determine an operating wavelength by geometrical dimensioning, to which a frequency range may correspond. This feature of magnetostatic waves results from the dispersive properties and from tuning by magnetic fields, which characteristics have no equivalent in the devices utilizing elastic waves where the speed of propagation of the Rayleigh waves is constant. In the sphere of magnetostatic wave devices, it is known that the magnetostatic waves of which the wavelength differs from an assigned value may be attenuated during transmission or reception by adopting a configuration in which the microtapes are folded into a U-shape. This technique is only applicable to a limited frequency range, since it presupposes that the currents flowing in the two branches of the U, spaced apart by .lambda./2, are in phase opposition.
The solutions which consist in making use of a configuration of transmission or reception transducers, such that transmission at the great magnetostatic wavelengths is diminished, have the disadvantage of introducing a delay which does not depend on the magnetic field establishing frequency tuning. In an arrangement comprising a tunable oscillator, this disadvantage tends to reduce the tuning range and to give rise to sudden mode variations.
The filter devices according to the invention enable alleviation of the disadvantages referred to in the foregoing.